Thermal degradation behavior of PLA composites containing bis DOPO phosphonates

Three novel bis 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) phosphonates including ethyl-bridged (DOPO2-ethyl), phenethyl-bridged (DOPO2-phenethyl), naphthalene-bridged (DOPO2-naphthalene) were synthesized and characterized. Thermal degradation properties of the synthesized compound alone and poly(lactic acid) (PLA) composites based on these compounds were examined by thermogravimetric. The kinetic parameters of PLA composites were calculated through Flynn-Wall-Ozawa method. The results showed that these derivatives had excellent thermal stability with start decomposition temperature above 360 °C, and with the increasing of aromatic rings in the molecular structure, the content of phosphaphenanthrene group remained in the condensed residues displayed an increase trend. Moreover, the thermal degradation behavior of PLA composites displayed significant dissimilarity to that of pure PLA. In addition, the activation energy increased from 51 kJ/mol of pure PLA to 141, 93, and 166 kJ/mol of PLA/DOPO2-ethyl, PLA/DOPO2-phenethyl, PLA/DOPO2-naphthalene, respectively, at 5% conversion, and these values increased to 179, 131 and 166 kJ/mol at 50% conversion, respectively.